1. Field of the Invention
The present invention relates to a CCD sensor output circuit of an image reading apparatus and more particularly, to improvements in a CCD sensor output circuit in an image reading apparatus, which detects, by a CCD sensor, the lights coming from a light source which are reflected by images in order to read the images.
2. Description of the Prior Art
FIG. 1 shows a conventional optical system in an image reading apparatus, to which one embodiment of the present invention applies. Referring to FIG. 1, lights from a white colored fluorescent lamp 3 are applied upon a color manuscript 2 with the color manuscript 2 arranged before a white-colored back plate 1. The lights from the white-colored fluorescent lamp 3, reflected by the color manuscript 2, are reflected by a mirror 4, focused, and input to a CCD sensor 6.
An image reading apparatus using a CCD sensor 6 as shown in FIG. 1 may be used in a facsimile OCR, a color scanner or the like. In such an image reading apparatus, the white-colored fluorescent lamp 3 is disadvantageous in that the radiation level changes due to differences in ambient temperatures or through rises in the guide temperature which is raised by self-heating after large amounts of lighting. As a measure to prevent these problems, methods have been adopted which use an automatic gain control circuit (AGC circuit) or flash a white-colored fluorescent lamp to change its lighting width thereby controlling the radiation amount. However, disadvantageously, a proper circuit is not provided which precisely controls a high-speed analog signal such as an AGC circuit. A method which varies the lighting width of the white-colored fluorescent lamp 3 becomes unstable in lighting when the lighting duty cycle becomes extremely small.